A variety of parallel optical communications modules exist for simultaneously transmitting and/or receiving multiple optical data signals over multiple respective optical data channels. Parallel optical transmitters have multiple optical transmit channels for transmitting multiple respective optical data signals simultaneously over multiple respective optical waveguides (e.g., optical fibers). Parallel optical receivers have multiple optical receive channels for receiving multiple respective optical data signals simultaneously over multiple respective optical waveguides. Parallel optical transceivers have multiple optical transmit and receive channels for transmitting and receiving multiple respective optical transmit and receive data signals simultaneously over multiple respective transmit and receive optical waveguides.
For each of these different types of parallel optical communications modules, a variety of designs and configurations exist. A typical layout for a parallel optical communications module includes an electrical subassembly (ESA) comprising a circuit board, such as a printed circuit board (PCB) with a ball grid array (BGA), and various electrical and optoelectronic components mounted on the upper surface of the circuit board, and an optical subassembly (OSA) comprising optical elements (e.g., refractive, reflective or diffractive lenses) mechanically coupled to the ESA. In the case of a parallel optical transmitter, laser diodes and one or more laser diode driver integrated circuits (ICs) are mounted on the circuit board. The circuit board has electrical conductors running through it (i.e., electrical traces and vias) and electrical contact pads on it. The electrical contact pads of the laser diode driver IC(s) are electrically connected to the electrical conductors of the circuit board. One or more other electrical components, such as a controller IC, for example, are typically also mounted on and electrically connected to the circuit board.
Similar configurations are used for parallel optical receivers, except that the circuit board of the parallel optical receiver has a plurality of photodiodes instead of laser diodes mounted on it and a receiver IC instead of a laser diode driver IC mounted on it. Parallel optical transceivers typically have laser diodes, photodiodes, one or more laser diode driver ICs, and a receiver IC mounted on it, although one or more of these devices may be integrated into the same IC to reduce part count and to provide other benefits.
The circuit board typically has one or more heat sink devices mounted on the upper surface thereof. The heat sink devices can have various shapes. The electrical and optoelectronic components are typically attached by a thermally conductive material to these heat sink devices to enable heat generated by them to pass down into the heat sink devices where the heat is dissipated or removed by some other means through the bottom of the circuit board. Heat sink devices all have the same general purpose of receiving heat generated by the respective components and absorbing and/or spreading out the heat to move it away from the components. Heat generated by the components can detrimentally affect the performance and life span of the parallel optical communications module.
In some designs, it is impossible or impractical to remove heat through the bottom of the circuit board. For example, with BGAs, the array of electrically-conductive balls on the bottom of the BGA are in contact with an array of electrical contacts of an external device, such as a mother circuit board. Because of these electrical connections, there may not be room for a heat dissipation path down through the bottom of the BGA. In such cases, it is known to remove heat through the top of the module by attaching an external heat dissipation device to the top of the module. In some cases, heat is dissipated through both the bottom of the circuit board and through the top of the module.
In some parallel optical communications modules, the upper surface of the circuit board is mechanically very fragile and electrically sensitive. In such cases, placing an external heat dissipation device in contact with the upper surface of the circuit board may damage the circuit board and/or detrimentally affect the electrical performance of the module. For example, the mechanical force exerted by the heat dissipation device may crack or warp the circuit board and/or damage the electrical traces of the circuit board, whereas the contact between the heat dissipation device and the circuit board may change the capacitance of the electrical traces leading to electrical performance problems.
Accordingly, a need exists for methods and systems that provide improvements in heat dissipation and that allow heat to be dissipated through the top of a parallel optical communications module without potentially damaging the circuit board or detrimentally affecting the performance of the module.